We have recently become aware of microRNAs (miRNAs) which appear to play a role in oncogenesis. Some of these miRNAs have the potential to become very promising targets for the development of cancer therapies. In this study, we examined some of the promising candidates identified in breast cancer; specifically miR-155 and the miR-17-92 cluster. We examined the potential of these targets to be affected by miRNA silencing techniques. The specific technique we used in this study relies on the use of antigomirs, or antisense miRNA molecules that have been shown to be effective in inhibiting miRNAs. We observed the effects of this prospective therapy in the mouse model of breast cancer. The results indicate that for the miR-155 target, the therapy is effective. Using luciferace imaging of mice, the tumor size was reduced compared to the control. Additionally, known targets of miR-155 (MAF and SHIP1) were shown to be upregulated compared to untreated control mice. Following these results, we also performed a microarray analysis, comparing the gene expression of treated tumor cells to that of non-tumor and untreated tumor cells. From this analysis, several new genes likely to interact with mir-155 were observed. Further studies should be carried out to determine the nature of these interactions and especially the interactions between them and cancer progression. The mir-17-92 cluster target failed to show the same exuberant results. Compared to the control, there is little or no reduction in tumor growth. No upregulation of mir-17-92 gene targets (E2F1, BIM and PTEN) was observed. It is not clear why there is a gap between the two objectives. Perhaps... middle of article...... which were previously not linked to breast cancer through the use of two-dimensional gel analysis. This study also identified protein expression patterns different from nucleic acid analysis (Wulfkuhle 2002). In another study, Adams et al. used a protein microarray to develop a protein expression model to differentiate between prostate cancers and benign prostatic hyperplasia. Such studies have paved the way for the discovery of new oncogenic protein markers (Bao-Ling Adam 2002). Through a different approach using biotanilation and mass spectroscopy analysis, another study was able to identify several proteins correlating with liver metastases (Borgia 2010). The approaches described above can be applied to our model. Although looking in this direction was beyond the scope of this study, it is the future direction of miR research-155..